Today, I will take you to Donghuan Malleable Iron Casting Co., Ltd. Let’s learn about the casting process of coated sand.
I. Knowledge and understanding of coated sand
1. Features of coated sand
It has suitable strength performance; good fluidity, the prepared sand molds and sand cores have clear contours and dense structures, which can produce complex sand cores; sand molds (cores) have good surface quality, and the surface roughness can reach Ra=6.3～12.5μm , The dimensional accuracy can reach CT7～CT9 level; the collapsibility is good, and the casting is easy to clean.
2. Scope of application
Coated sand can be used to make molds and sand cores. The molds or cores of coated sand can be used in conjunction with each other or with other sand molds (cores); it can not only be used for metal gravity casting or low-pressure casting, but also It can be used for sand-coated iron casting and thermal centrifugal casting; it can be used not only for the production of cast iron and non-ferrous alloy castings, but also for the production of steel castings.
II. Preparation of coated sand
1. Composition of coated sand
It is generally composed of refractory materials, binders, curing agents, lubricants and special additives.
2. Production process of coated sand
The preparation process of coated sand mainly includes cold coating, warm coating, and thermal coating. At present, almost all the production of coated sand adopts the hot coating method.
3. Main product types of coated sand
(1) Ordinary coated sand is traditional coated sand
(2) High-strength and low-gassing type coated sand
Features: high strength, low expansion, low gas, slow gas, anti-oxidation
(3) High temperature resistant (type) coated sand (ND type)
Features: high temperature resistance, high strength, low expansion, low gas, slow gas, easy to collapse, anti-oxidation
(4) Easily collapsible coated sand
It has good strength and excellent low-temperature collapse performance, suitable for the production of non-ferrous metal castings.
(5) Other special requirements coated sand.
III. The main process of core making with coated sand
The heating temperature is 200-300℃, the curing time is 30-150s, and the sand shooting pressure is 0.15-0.60MPa. For sand cores with simple shapes and coated sand with good fluidity, lower shooting pressure can be selected. For thin sand cores, a lower heating temperature can be selected. When the heating temperature is low, the curing time can be appropriately extended. The resin used in coated sand is phenolic resin. The advantages of the core-making process: suitable strength performance; good fluidity; good surface quality of the sand core (Ra=6.3-12.5μm); strong moisture resistance of the sand core; good collapsibility and easy cleaning of castings.
1. Mold (mold) temperature
The mold temperature is one of the main factors affecting the thickness and strength of the shell layer, generally controlled at 220～260℃
2. Sand shooting pressure and time
The sand shooting time is generally controlled at 3～10s. If the time is too short, the sand mold (core) cannot be formed. The sand shooting pressure is generally about 0.6MPa; when the pressure is too low, it is easy to cause insufficient shooting or looseness. Hardening time: The length of hardening time mainly depends on the thickness of the sand mold (core) and the temperature of the mold, generally around 60-120s.
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Post time: Dec-22-2021